Power transmission belts comprising an elastomeric body reinforced with one or more helical winds of a cord, such as fiber glass strand and the like which are treated and/or coated to bond to the elastomer to thus form a tension member are well known in the art. Some belts include lateral members which provide lateral stiffness to the belt while permitting longitudinal flexibility for use to transmit power in variable pulley drives. Belts of this nature perform this function by engaging the pulley flanges with its edges. In the absence of the stiffeners, belts in such drives become arched and distort laterally with less than predictable results. Examples of belts with lateral stiffening means are described in U.S. patents to Unger and Redmond U.S. Pat. Nos. 2,189,049 and 3,772,929, respectively.